Speech Intelligibility Index and Lexical Ability
Stiles, Bentler, and McGregor (2012) note that children with hearing loss (CHL) have smaller vocabularies, often learn fewer novel words, and generally have greater word learning deficits, than do children with normal hearing (CNH). Further, with regard to lexical ability (i.e., the ability to acquire and learn words, meaning, and language), it has been demonstrated that age at intervention matters. That is, with regard to five-year-old children with mild-to-profound hearing loss, those who received earlier rehabilitation demonstrated greater receptive vocabularies. Of note, although degree-of-hearing-loss (typically based on a three frequency pure tone average, PTA) is a compelling factor with regard to language outcome, individual differences are vast and are not clearly or consistently predictive of language outcome.
Stiles, Bentler, and McGregor report the PTA does not represent the aided listening condition in which CHL obtain the majority of their language experience. However, they report the Speech Intelligibility Index (SII) can quantify (via free, downloadable software) speech audibility and can "factor in the amplification characteristics of the hearing aid and may prove to be more consistent in predicting language development…." As has been often reported, children require greater audibility than do adults, to achieve "adult-like" performance.
In their study, the authors initially evaluated 18 children with hearing loss and 28 children with normal hearing. Their final data set included 40 children (16 CHL and 24 CNH). With regard to word recognition scores (WRSs) the aided SII and the PTA were about equal with regard to predicting WRSs. However, with regard to lexical ability, the aided SII performed better than the PTA with regard to accounting for individual differences, likely due to the fact that it addresses aided long term speech audibility.
For More Information, References, and Recommendations
Stiles DJ, Bentler RA, McGregor KK. (2012) The Speech Intelligibility index and the Pure-Tone Average as Predictors of Lexical Ability in Children Fit With Hearing Aids. Journal of Speech, Language, and Hearing Research. 55(June):764-778.